This invention relates to apparatus for compressively treating traveling flexible sheet material, more particularly to mechanism of such apparatus which compresses the material against the surface of a drive roll preliminary to its engagement with a retarding surface.
Apparatus of the type concerned is exampled by U.S. Pat. Nos. 3,260,778; 3,416,192; 3,810,280; 4,090,385 and other U.S. patents similar thereto. It is capable of compressively treating the material to produce therein what is generally known as "microcreping", of variable form and extent, depending on nature and adjustment of specific mechanisms, with corresponding variable desirable physical changes in the material which are described in the patents.
In such apparatus, a variable pressure device applies pressure to an assembly of sheet members extending across the path of travel of the material on a rotating drive roll, to compress the material against the surface of the drive roll before the material engages a retarding surface. The nature and extent of the compressive force so exerted on the material are critical in the operation of the apparatus, in that they determine the forward thrust exerted on the material as it engages the retarder surface and the degree of its simultaneous expansion, which are major factors in the treatment. The pressure needs to be resiliently applied, adjustable within limits to suit different materials or desired effects while always avoiding excessive pressure which could damage or undesirably mark the material.
To meet these exacting requirements, the pressure is applied through an assembly of sheet members extended across the width of the material. This assembly includes an inner member closest to the drive roll, commonly called the "primary member" or "primary blade," and an outer member. These are usually of thin spring steel, they may have one or more like members between them and they have been fixedly clamped to the holder means at the region of their edge disposed rearwardly in the direction of travel of the material, so that they form a cantilever from that edge region and are prevented from moving laterally or longitudinally relative to one another. The assembly of sheet members also normally includes one that has its rearward edge in the direction of travel inserted between two of the other sheet members of the assembly, so it is held thereby, without attachment to the holder means. The forward edge of this one sheet member is spaced forwardly of the forward edge of the primary member and has surface engagement with the material advancing beyond the forward edge of the primary member. The material-engaging surface of this one member may be smooth to engage the material and confine it against a retarding surface on the opposite side of the material; or, this surface may be somewhat roughened, to act itself as the retarding surface.
The outer member of this assembly of sheet members is engaged across the width of the material on the roll by a shoe of a variable pressure applying means. The shoe engages the outer sheet member in the cantilevered forward portion of the assembly, usually closely behind the forward edge of the primary member, to flex the free forward portion of the assembly, so that a forward end portion of the inner surface of the primary member is forced against the material on the drive roll with an applied pressure of up to about 100 pounds per linear inch. The pressure means and holder means are mounted for movement longitudinally of the direction of travel of the material into and out of operative position and for adjustment of relative position in that direction.
This combination of mechanisms for applying pressure to the material on the drive roll has worked well and become standard, despite the wide variety of materials which the apparatus is capable of processing. However, it has encountered a serious difficulty due to heat generated in the primary sheet member by the friction of the compressed material slid under it by the drive roll, in turn heating the rest of the assembly. Particularly with materials of high surface friction coefficients, the heat so induced can run as high as 400.degree. F. to 450.degree. F. This results in time in distortion of the primary member with an irregular buckling or corrugation of its material-contacting area, which interferes with its function and is prone to produce unacceptable visible streaking in the material. To mitigate this difficulty, elaborate systems for cooling the assembly have been devised and used. These cooling systems have reduced the adverse effects of the generated heat somewhat but they are not adequately effective in many cases, particularly at the higher temperatures. They are also costly to make and operate.